在51nod刷到过同样的题，直接秒杀
见https://blog.csdn.net/qq_34416123/article/details/81697683
#include<cstdio>
#include<cstring>
#include<algorithm>
#define REP(i, a, b) for(int i = (a); i < (b); i++)
using namespace std;const int MAXN = 1123;
char a[MAXN], b[MAXN];
int f[MAXN][MAXN], path[MAXN][MAXN];void print(int x, int y)
{if(path[x][y] == 1){print(x - 1, y - 1);putchar(a[x]);}else if(path[x][y] == 2) print(x - 1, y);else if(path[x][y] == 3)print(x, y - 1);
}int main()
{scanf("%s%s", a + 1, b + 1);int lena = strlen(a + 1), lenb = strlen(b + 1);REP(i, 1, lena + 1)REP(j, 1, lenb + 1){if(a[i] == b[j]) {f[i][j] = f[i-1][j-1] + 1;path[i][j] = 1;}else if(f[i-1][j] > f[i][j-1]){f[i][j] = f[i-1][j];path[i][j] = 2;}else{f[i][j] = f[i][j-1];path[i][j] = 3;}}printf("%d\n", f[lena][lenb]);print(lena, lenb);return 0;
}